#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <sys/epoll.h>
#include <fcntl.h>
#include <errno.h>

#define BUF_SIZE 4
#define EPOLL_SIZE 50

void setnonblockingmode(int fd);
void error_handling(char *message);

int main(int argc, char *argv[])
{
  int serv_sock, clnt_sock;
  struct sockaddr_in serv_adr, clnt_adr;
  socklen_t adr_sz;
  int str_len, i;
  char buf[BUF_SIZE];

  struct epoll_event *ep_events;
  struct epoll_event event;
  int epfd, event_cnt;
  if (argc != 2)
  {
    printf("Usage : %s <port> \n", argv[0]);
    exit(1);
  }
  
  serv_sock = socket(PF_INET, SOCK_STREAM, 0);
  if (serv_sock == -1)
    error_handling("socket() error!");
  memset(&serv_adr, 9, sizeof(serv_adr));
  serv_adr.sin_family = AF_INET;
  serv_adr.sin_addr.s_addr = htonl(INADDR_ANY);
  serv_adr.sin_port = htons(atoi(argv[1]));

  if (bind(serv_sock, (struct sockaddr *) &serv_adr, sizeof(serv_adr)) == -1)
    error_handling("bind() error!");

  if (listen(serv_sock, 5) == -1)
    error_handling("listen() error!");

  epfd = epoll_create(EPOLL_SIZE);
  ep_events = malloc(sizeof(struct epoll_event) * EPOLL_SIZE);

  setnonblockingmode(serv_sock);
  event.events = EPOLLIN;
  event.data.fd = serv_sock;
  epoll_ctl(epfd, EPOLL_CTL_ADD, serv_sock, &event);

  while (1)
  {
    event_cnt = epoll_wait(epfd, ep_events, EPOLL_SIZE, -1);
    if (event_cnt == -1)
    {
      puts("epoll_wait() error");
      break;
    }

    puts("return epoll_wait");
    for (i = 0; i < event_cnt; i++)
    {
      if (ep_events[i].data.fd == serv_sock) 
      {
        adr_sz = sizeof(clnt_adr);
        clnt_sock = accept(serv_sock, (struct sockaddr *) &clnt_sock, &adr_sz);
        setnonblockingmode(clnt_sock);
        event.events = EPOLLIN | EPOLLET;
        event.data.fd= clnt_sock;
        epoll_ctl(epfd, EPOLL_CTL_ADD, clnt_sock, &event);
        printf("connected client: %d \n", clnt_sock);
      }
      else
      {
        while(1)
        {
          str_len = read(ep_events[i].data.fd, buf, BUF_SIZE);
          if (str_len == 0)
          {
            epoll_ctl(epfd, EPOLL_CTL_DEL, ep_events[i].data.fd, NULL);
            close(ep_events[i].data.fd);
            printf("closed client: %d \n", ep_events[i].data.fd);
            break;
          }
          else if(str_len<0)
          {
            if (errno == EAGAIN)
              break;
          }
          else
          {
            write(ep_events[i].data.fd, buf, str_len);
          }
        }
      }
    }
  }
  close(serv_sock); close(epfd);
  return 0;
}

void error_handling(char *message)
{
  fputs(message, stderr);
  fputs("\n", stderr);
  exit(1);
}

void setnonblockingmode(int fd)
{
  int flag = fcntl(fd, F_GETFL, 0);
  fcntl(fd, F_SETFL, flag|O_NONBLOCK);
}
